As pointed out, induction hardened valve seats were used in cars meant for use with unleaded gas. Valve seat recession ( premature wear)was a problem using unleaded gas in cars designed for leaded fuel. However, after the introduction of unleaded fuel, it became apparent that the valve seat issue was not as bad as expected, and only vehicles under heavy duty usage were showing valve seat problems. Although nothing solved the problem as well as lead additives, it has since been observed that other additives such as top cylinder oils help prevent valve seat recession. Some octane boosters also claim to prevent valve seat problems. Top cylinder oils are added by the refiners to some premium grade gasolines to help keep fuel deposits off of intake valve tulips. You can add your own to your gas if you wish; Marvel Mystery Oil is a top cylinder oil, and is widely sold at auto supply stores.
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